This study investigated the anti-acne activity of botanical extracts from a plant used traditionally by Native Americans. Extracts of the plant's leaves and essential oils showed the highest inhibition of Propionibacterium acnes, the bacteria that causes acne. Further separation of the leaf extract found that the hexane and ethyl acetate partitions were even more effective at inhibiting P. acnes than the original crude extract. The leaf essential oil demonstrated stronger antimicrobial properties against P. acnes than tea tree oil. Future work will refine the most active extracts and test their safety on human skin cells.

1. An Investigation into the Anti-Acne Activity of Botanical Extracts
Rina Lee1,2*, Kate Nelson2, James T. Lyles1, Cassandra L. Quave1,2
1Center for the Study of Human Health, Emory University, Atlanta, GA; 2Department of Dermatology, Emory University School of Medicine, Atlanta, GA;
*E-mail: nwlee@emory.edu Lab Website: http://etnobotanica.us/
This work was supported by Dr. Quave’s research development funds. Special thanks to Justin Robeny for
helping with the preparation of the extracts, and Xena Huang for helping with the growth inhibition assay.
1. Perry, A. and P. Lambert (2011). "Propionibacterium acnes: infection beyond the skin."
Expert Rev Anti Infect Ther 9(12): 1149-1156.
2. van Valen, R., et al. (2016). "Prosthetic valve endocarditis due to Propionibacterium acnes."
Interact Cardiovasc Thorac Surg.
3. Dinant, A. and R. A. Boulos (2016). "Zolav((R)): a new antibiotic for the treatment of
acne." Drug Des Devel Ther 10: 1235-1242.
ABSTRACT
Propionibacterium acnes (Fig.1) is a Gram-positive anaerobe and is commonly found on the skin, oral cavity,
and large intestine, as part of our normal flora.1 P. acnes is an opportunistic pathogen and has been known to
cause cerebral, ocular, spinal, and postsurgical infections.2 The pathogen is most associated with the common
skin condition called acne vulgaris (Fig.2). While acne vulgaris is not a life-threatening condition, it affects 80%
of teenagers and young adults, which translates to approximately 650 million people across the globe. The exact
mechanism of P. acnes in causing acne vulgaris is currently unknown. However, P. acnes causes an
inflammatory response in the skin by blocking pilosebaceous follicles (Fig.3). The current treatments used
include topical and oral therapies, and the antibiotics erythromycin and clindamycin are used in more severe
cases.3 Based on previous bioassay screening, we discovered that a particular plant, with a long history of
traditional use by Native Americans, inhibits the growth of P. acnes. My project for this semester was to
investigate further into the anti-acne activity of this particular plant.
RESEARCH AIMS
My research goal for this semester was to examine several botanical extracts, which are the various parts of the
same plant, and conduct further screening to determine the most active plant part against P. acnes.
REFERENCES
METHODS
RESULTS
FUNDING&
THANKS
FIG. 1. P. acnes FIG.2. Acne vulgaris FIG.3. Progression of acne formation
Whole Plant
649: Leaves
649B:
Hexane
649C: Ethyl
Acetate
649D:
Butanol
649E:
Water
650: Leaf
Essential Oil
651: Stems
652: Mature
Fruits
653: Immature
Fruits
Table 3 MIC50 (µg/mL) MIC90 (µg/mL)
649 64 64
651 ND (256) ND (256)
652 ND (256) ND (256)
653 ND (256) ND (256)
Erythromycin 0.03125 0.125
Clindamycin 0.0625 0.5
-60
-40
-20
0
20
40
60
80
100
120
1 10 100 1000
%Inhibition
Log Concentration (µg/mL)
Effectiveness of Crude Extracts
against P. acnes
649
651
652
653
-30
-10
10
30
50
70
90
110
130
1 10 100 1000
%Inhibition
Log Concentration (µg /mL)
Effectiveness of Partitioned Extracts
against P. acnes
649B
649C
649D
649E
c
Table 4 MIC50 (µg/mL) MIC90 (µg/mL)
649B 16 32
649C 32 64
649D ND (256) ND (256)
649E ND (256) ND (256)
650 0.0016% v/v 0.0032% v/v
Tea Tree 0.0128% v/v 0.0256% v/v
FIG.6.
Hexane
partition
(649B) in a
separatory
funnel.
FIG.5. Wet
distillation
for extract
650.
649B 649C Ery Clin
FIG.7. 96-
well plate
shows P.
acnes
inhibition.
FIG.4.
Lyophilized
crude extract
652.
0
20
40
60
80
100
120
0 1 2 3 4 5
%Inhibition
Concentration (µg/mL)
Effectiveness of Controls against P.
acnes
Erythromycin
Clindamycin
FIG.9 a) the percent
inhibition of the crude
extracts against P.
acnes b) the
absorbance readings of
Extract 650 and tea
tree oil after 72 hours
of P. acnes incubation
(* p < 0.05, †
p < 0.01,
‡
p < 0.001)
c) the percent
inhibition of the leaf
partitions against P.
acnes d) the percent
inhibition of antibiotics
Erythromycin and
Clindamycin, which
were the positive
controls.
a
d
CONCLUSIONS
v The leaf extract (649) and leaf essential oil were the
most active in inhibiting the growth of P. acnes.
v The hexane (649B) and ethyl acetate (649C)
partitions of the leaf extract were even more active
against P. acnes than the crude leaf extract.
v The leaf essential oil (650) is significantly more
active than tea tree oil, which has antimicrobial
properties, against P. acnes.
FIG.8. Extraction Scheme
Tables 3 & 4 Summary of the 50% and
90% minimum inhibitory concentrations.
Table 1
649
256 µg/mL 128 µg/mL 64 µg/mL 32 µg/mL
651 ‡
‡
‡
652 ‡
‡
‡
653 ‡
‡
†
*
Table 2
649 649B 649C 649D 649E
649
* †
‡
‡
649B
‡
‡
‡
649C
‡
†
649D
649E
Table 1 & 2 T-test results comparing extracts to
each other (* p < 0.05, †
p < 0.01, ‡
p < 0.001)
FUTURE DIRECTIONS
v Run flash chromatography on the hexane
partition, ethyl acetate partition, and the leaf
essential oil to further refine the extracts.
v Run a cytotoxicity assay against human
keratinocytes to test general toxicity.
Dry plant
material
Make crude
extracts
Liquid-liquid
partitioning
Extract
essential oil
Growth
Inhibition
Assay
y = -0.17ln(x) - 0.4986
R² = 0.9496
y = -0.038ln(x) + 0.6316
R² = 0.31456
0
0.2
0.4
0.6
0.8
1
1.2
0 0.01 0.02 0.03
Absorbanceat600nm
% Volume by Oil
Extract 650 vs. Tea tree oil: Growth
Inhibition of P. acnes
650
Tea tree oil
‡
*
‡
‡
‡